Generally, self-embedded power supplies are configured in various vehicles, apparatus, or electronic devices to provide electric energy to various internal components. For example, a storage battery, usually a lead-acid battery, is normally installed in a car to provide electric energy necessary to start the car. Besides, the storage battery can also be used as a low-voltage DC power supply to provide other electronic devices in a car, such as stereo, air conditioner, light, instrumentation, etc. with low-voltage DC power. Usually, after being started, the engine of a car can charge a car battery to ensure sufficient power of the car battery. However, due to reasons such as being shut down for a long time, leaving the key switch open, leaving the lights on after turning off the engine, or malfunction of the low-voltage electric system of the vehicle, the car battery may not have sufficient power to start a car. Therefore, some emergency power supply products are used in cars to provide emergency starting when the car battery is unable to start the car.
However, according to different rating voltage specifications, common automobile storage batteries are divided into 12V and 24V batteries which can respectively start gasoline engines and diesel engines. Storage batteries with different rating voltages require different charging circuits, otherwise excessive voltage will overheat, or even damage, the battery, while insufficient voltage cannot effectively charge the battery. In the prior art, storage batteries with different rating voltage specifications usually adapt to different emergency power supplies, which are incompatible and causes inconvenience and a waste of resources. Besides, under special circumstances, self-embedded power supplies are not installed in vehicles, apparatus, or electronic devices, which raises the need for compatible external emergency power supplies which provide multi-voltage output.
In addition, it is desirable that emergency power supplies might also be charged. It is desirable to provide a solution of charging a multi-voltage output emergency power supply based on the energy storage status of respective energy storage modules.